This invention relates to a method of dispersing a tacky additive into a solution of a polymer, particularly a polyalphaolefin. In particular, it relates to the addition of the additive to a slurry comprised of a non-polar solvent and an insoluble, infusible, non-reactive dispersant, followed by the addition of the resultant slurry to a separate polymer solution.
Polyethylene can be produced by a gas phase process, a slurry process, or a solution process. In a gas phase process, the polymerization is conducted in the absence of any solvent. In a slurry process, polymerization takes place in a diluent at a temperature below the melting point of the polymer, producing solid polymer particles suspended in the diluent.
In a solution process for preparing polyethylene, polymerization of ethylene takes place in a non-polar solvent above the melting point of the polymer, producing a solution of the polymer. The polymer is recovered by evaporating the solvent and unreacted monomer. A solution process permits a shorter transition time between products which reduces the cost of changing product and permits a broader line of products to be produced. Also, in a solution process, products can be produced with a lower molecular weight and a lower density than can be obtained with a slurry process.
Various additives can be added to the polymer solution prior to separation of the polymer from the solvent to prevent degradation of the polymer during processing and/or during use by the consumer. For example, UV light stabilizers can be added to prevent the finished part from being rapidly degraded by ultraviolet light. In the solution process, all of these additives must be either dissolved in a suitable solvent or finely suspended in a solvent prior to their injection into the solution of the polymer.
However, certain additives (herein referred to as "tacky additives") are not soluble in a suitable solvent nor are they entirely insoluble in the solvent. Instead, they become soft and sticky when contacted by the solvent even though these additives exist as free flowing particles in a dry form. These tacky additives adhere to the walls of the vessel, to the impeller and to themselves, producing large elastic spheres which plug up the additive nozzle. As a result, the additive is not incorporated into the polymer stream. This results in a polymer which does not meet specifications since it does not contain the desired level of additive. Furthermore, the vessel must be shut down and cleaned periodically, which is a difficult and time-consuming process.